IPv6 WG M. Crawford
Internet-Draft Fermilab
Expires: August 17, 2006 B. Haberman, Ed.
JHU APL
February 13, 2006
IPv6 Node Information Queriesdraft-ietf-ipngwg-icmp-name-lookups-15
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document describes a protocol for asking an IPv6 node to supply
certain network information, such as its hostname or fully-qualified
domain name. IPv6 implementation experience has shown that direct
queries for a hostname are useful, and a direct query mechanism for
other information has been found useful in serverless environments
and for debugging.
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This document specifies a mechanism for discovering information about
names and addresses. The applicability of these mechanisms is
currently limited to diagnostic and debugging tools and network
management (e.g. node discovery). In the global internet, the Domain
Name System[1][2] is the authoritative source of such information and
this specification is not intended to supplant or supersede it. And
in fact, in a well-supported network, the names and addresses dealt
with by this mechanism will be the same ones, and with the same
relationships, as those listed in the DNS.
This new Node Information protocol does provide facilities which are
not found in the DNS - for example discovering relationships between
addresses without reference to names. And the functions that do
overlap with the DNS may be useful in serverless environments, for
debugging, or in regard to link-local and unique-local addresses [3]
which often will not be listed in the DNS.
2. Applicability Statement
IPv6 Node Information Queries include the capability to provide
forward and reverse name lookups independent of the DNS by sending
packets directly to IPv6 nodes or groups of nodes.
The applicability of these mechanisms is currently limited to
diagnostic and debugging tools and network management (e.g. node
discovery). These mechanisms can be used to learn the addresses and
names for nodes on the other end of a point-to-point link or nodes on
a shared-medium link such as an Ethernet. This is very useful when
debugging problems or when bringing up IPv6 service where there isn't
global routing or DNS name services available. IPv6's large auto-
configured addresses make debugging network problems and bringing up
IPv6 service difficult without these mechanisms. An example of an
IPv6 debugging tool using IPv6 Node Information Queries is the ping6
program in the KAME (<http://www.kame.net>), USAGI, and other IPv6
implementations.
The mechanisms defined in this document may have wider applicability
in the future, but any use beyond debugging and diagnostic tools is
left for further study and is beyond the scope of this document.
3. Terminology
A "Node Information (or NI) Query" message is sent by a "Querier"
node to a "Responder" node in an ICMPv6 packet addressed to the
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* 139 - NI Query
* 140 - NI Reply
o Code
* For NI Query
+ 0 - Indicates that the Data field contains an IPv6 address
which is the Subject of this Query.
+ 1 - Indicates that the Data field contains a name which is
the Subject of this Query, or is empty, as in the case of a
NOOP.
+ 2 - Indicates that the Data field contains an IPv4 address
which is the Subject of this Query.
* For NI Reply
+ 0 - Indicates a successful reply. The Reply Data field may
or may not be empty.
+ 1 - Indicates that the Responder refuses to supply the
answer. The Reply Data field will be empty.
+ 2 - Indicates that the Qtype of the Query is unknown to the
Responder. The Reply Data field will be empty.
o Checksum - The ICMPv6 checksum.
o Qtype - A 16-bit field which designates the type of information
requested in a Query or supplied in a Reply. Its value in a Reply
is always copied from the corresponding Query by the Responder.
Five values of Qtype are specified in this document.
o Flags - Qtype-specific flags which may be defined for certain
Query types and their Replies. Flags not defined for a given
Qtype must be zero on transmission and ignored on reception, and
must not be copied from a Query to a Reply unless so specified in
the definition of the Qtype.
o Nonce - An opaque 64-bit field to help avoid spoofing and/or to
aid in matching Replies with Queries. Its value in a Query is
chosen by the Querier. Its value in a Reply is always copied from
the corresponding Request by the Responder.
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o Data - In a Query, the Subject Address or Name. In a Reply,
Qtype-specific data is present only when the ICMPv6 Code field is
zero. The length of the Data may be inferred from the IPv6
header's Payload Length field[6], the length of the fixed portion
of the NI packet and the lengths of the ICMPv6 header and
intervening extension headers.
Note that the type of information present in the Data field of a
Query is declared by the ICMP Code, while the type of information, if
any, in the Data field of a Reply is determined by the Qtype.
When the Subject of a Query is a name, the name MUST be in DNS wire
format [2]. The name may be either a fully-qualified domain name,
including the terminating zero-length label, or a single DNS label
followed by two zero-length labels. Since a Query contains at most
one name, DNS name compression MUST NOT be used.
5. Message Processing
The Querier constructs an ICMP NI Query and sends it to the address
from which information is wanted. When the Subject of the Query is
an IPv6 address, that address will normally be used as the IPv6
destination address of the Query, but need not be if the Querier has
useful a priori information about the addresses of the target node.
An NI Query may also be sent to a multicast address of link-local
scope [3].
When the Subject is a name, either fully-qualified or single-
component, and the Querier does not have a unicast address for the
target node, the query MUST be sent to a link-scope multicast address
formed in the following way. The Subject Name is converted to the
canonical form defined by DNS Security [7], which is uncompressed
with all alphabetic characters in lower case. (If additional DNS
label types or character sets for host names are defined, the rules
for canonicalizing those labels will be found in their defining
specification.) Compute the MD5 hash [8] of the first label of the
Subject Name -- the portion beginning with the first one-octet length
field and up to, but excluding, any subsequent length field. Append
the first 24 bits of that 128-bit hash to the prefix FF02:0:0:0:0:2:
FF00::/104. The resulting multicast address will be termed the "NI
Group Address" for the name. A node will support an "NI Group
Address" for each unique single-label name.
The Nonce MUST be a random or good pseudo-random value to foil
spoofed replies. An implementation which allows multiple independent
processes to send NI queries MAY use the Nonce value to deliver
Replies to the correct process. Nonetheless, such processes MUST
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check the received Nonce and ignore extraneous Replies.
If true communication security is required, IPsec [14] should be
used. Providing the infrastructure to authenticate NI Queries and
Replies may be quite difficult outside of a well-defined community.
Upon receiving an NI Query, the Responder must check the Query's IPv6
destination address and discard the Query without further processing
unless it is one of the Responder's unicast or anycast addresses, or
a link-local scope multicast address which the Responder has joined.
Typically the latter will be an NI Group Address for a name belonging
to the Responder. A node MAY be configured to discard NI Queries to
multicast addresses other than its NI Group Address(es) but if so,
the default configuration SHOULD be not to discard them.
A Responder must also silently discard a Query whose Subject Address
or Name (in the Data field) does not belong to that node. A single-
component Subject Name matches any fully-qualified name whose first
label matches the Subject. All name matching is done in a case-
independent manner consistent with DNSSEC name canonicalization [7].
Next, if Qtype is unknown to the Responder, it must return an NI
Reply with ICMPv6 Code = 2 and no Reply Data. The Responder should
rate-limit such replies as it would ICMPv6 error replies [5].
Next, the Responder should decide whether to refuse an answer, based
on local policy. (See "Security Considerations" for recommended
default behavior.) If an answer is refused, depending on local
policy the Responder can elect to silently discard the query or send
an NI Reply with ICMPv6 Code = 1 and no Reply Data. Again, the
Responder should rate-limit such replies as it would ICMPv6 error
replies [5].
Finally, if the Qtype is known and the response is allowed by local
policy, the Responder MUST fill in the Flags and Reply Data of the NI
Reply in accordance with the definition of the Qtype and transmit the
NI Reply. The source address of the NI Reply SHOULD be selected
using the rules defined in [9].
If the Query was sent to a multicast address, transmission of the
Reply MUST be delayed by a random interval between zero and [Query
Response Interval], as defined by Multicast Listener Discovery
Version 2 [10].
6. Defined Qtypes
The following Qtypes are defined. Qtypes 0, 2, and 3 MUST be
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supported by any implementation of this protocol. Qtype 4 SHOULD be
supported by any implementation of this protocol on an IPv4/IPv6
dual-stack node and MAY be supported on an IPv6-only node.
+-------------+----------------+
| Qtype Value | Qtype Name |
+-------------+----------------+
| 0 | NOOP |
| 1 | unused |
| 2 | Node Name |
| 3 | Node Addresses |
| 4 | IPv4 Addresses |
+-------------+----------------+
6.1. NOOP
This NI type has no defined flags and never has a Data field. A
Reply to an NI NOOP Query tells the Querier that a node with the
Queried Address is up and reachable and implements the Node
Information protocol. On transmission, the ICMPv6 Code in a NOOP
Query must be set to 1 and the Code in a NOOP Reply must be 0. On
reception of a NOOP Query or Reply, the Code must be ignored.
6.2. Node Name
The NI Node Name Query requests the fully-qualified or single-
component name corresponding to the Subject Address or Name. The
Reply Data has the following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Node Names ... |
+ +
/ /
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Node Information Reply Message
o TTL - MUST be zero. Any non-zero value received MUST be treated
as zero. This field is no longer used but is present to preserve
backwards compatibility with older implementations.
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o Node Names - The fully-qualified or single-component name or names
of the Responder which correspond(s) to the Subject Address or
Name, in DNS wire format, Section 3.1 of [2]. Each name MUST be
fully-qualified if the responder knows the domain suffix, and
otherwise be a single DNS label followed by two zero-length
labels. When multiple node names are returned and more than one
of them is fully-qualified, DNS name compression, Section 4.1.4 of
[2], SHOULD be used, and the offsets are counted from the first
octet of the Data field. An offset of 4, for example, will point
to the beginning of the first name.
The Responder must fill in the TTL field of the Reply with zero.
Only one TTL is included in the reply.
If the Responder does not know its name at all it MUST send a Reply
with TTL=0 and no Node Names (or a Reply with Code=1 indicating
refusal to answer). The Querier will be able to determine from the
packet length that the Data field contains no names.
6.3. Node Addresses
The NI Node Addresses Query requests some set of the Responder's IPv6
unicast addresses. The Reply Data is a sequence of 128-bit IPv6
addresses, each address preceded by a separate 32-bit TTL value, with
Preferred addresses listed before Deprecated addresses [11], but
otherwise in no special order. Five flag bits are defined in the
Query, and six in the Reply.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Qtype=3 | unused |G|S|L|C|A|T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Node Information Address Query
o G - If set to 1, Global-scope addresses [12] are requested.
o S - If set to 1, Site-local addresses [12] are requested.
However, Site-local addresses are now deprecated [15] and this
flag is for backwards compatibility.
o L - If set to 1, Link-local addresses [12] are requested.
o C - If set to 1, IPv4-compatible (now deprecated) and IPv4-mapped
addresses [3] are requested. Responses SHOULD include IPv4
addresses in IPv4-mapped form.
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o A - If set to 1, all the Responder's unicast addresses (of the
specified scope(s)) are requested. If 0, only those addresses are
requested which belong to the interface (or any one interface)
which has the Subject Address, or which are associated with the
Subject Name.
o T - Defined in a Reply only, indicates that the set of addresses
is incomplete for space reasons.
Flags G, S, L, C and A are copied from a Query to the corresponding
Reply.
The TTL associated with each address MUST be zero.
6.4. IPv4 Addresses
The NI IPv4 Addresses Query requests some set of the Responder's IPv4
unicast addresses. The Reply Data is a sequence of 32-bit IPv4
addresses, each address preceded by a 32-bit TTL value. One flag bit
is defined in the Query, and two in the Reply.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Qtype=4 | unused |A|T|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Node Information IPv4 Address Query
o A - If set to 1, all the Responder's unicast addresses are
requested. If 0, only those addresses are requested which belong
to the interface (or any one interface) which has the Subject
Address.
o T - Defined in a Reply only, indicates that the set of addresses
is incomplete for space reasons.
Flag A is copied from a Query to the corresponding Reply.
The TTL associated with each address MUST be zero.
6.4.1. Discussion
It is possible that a node may treat IPv4 interfaces and IPv6
interfaces as distinct, even though they are associated with the same
hardware. When such a node is responding to an NI Query having a
Subject Address of one type requesting the other type, and the Query
has the A flag set to 0, it SHOULD consider IP interfaces, other than
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tunnels, associated with the same hardware as being the same
interface.
7. IANA Considerations
ICMPv6 type values 139 and 140 were previously assigned by IANA for
this protocol. This document defines three values of the ICMPv6 Code
field for each of these ICMPv6 Type values. Additional Code values
may be defined using the "Specification Required" criteria from [16].
IANA is requested to establish and maintain a registry for the Code
fields associated with the Node Information Query ICMPv6 Types as a
part of its ICMPv6 Registry updated in [13].
This document defines five values of Qtype, numbers 0 through 4.
Following the policies outlined in [16], new values, and their
associated Flags and Reply Data, are to be defined by IETF Consensus.
The IANA is requested to assign the IPv6 multicast prefix FF02:0:0:0:
0:2:FF00::/104 for use in Node Information Queries as defined in
Section 5. It should be noted that this request does conform with
the requirements defined in [17].
8. Security Considerations
This protocol shares the security issues of ICMPv6 that are
documented in the "Security Considerations" section of [5].
This protocol has the potential of revealing information useful to a
would-be attacker. An implementation of this protocol MUST have a
default configuration which refuses to answer queries from global-
scope [3] addresses.
Implementations SHOULD apply rate-limiting to NI responses to avoid
being used in a denial of service attack.
The anti-spoofing Nonce does not give any protection from spoofers
who can eavesdrop the Query or the Reply.
The information learned via this protocol SHOULD not be trusted for
making security relevant decisions unless some other mechanisms
beyond the scope of this document is used to authenticate this
information.
An implementation of this protocol SHOULD provide the ability to
control the dissemination of information related to IPv6 Privacy
Addresses [18]. The default action of this policy SHOULD NOT provide
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a response to a Query that contains a node's Privacy Addresses.
A node MUST NOT include Privacy Addresses in any Node Addresses
response which includes a public address, or for which the source
address of the response, the destination address of the request, or
the Subject Address of the request, is a public address. Similarly,
a node MUST NOT include any address other than the (single) Privacy
Address in any Node Addresses response which includes the Privacy
Address, or for which the source address of the response, the
destination address of the request, or the Subject Address of the
request, is the Privacy Address.
9. Acknowledgments
Alain Durand contributed to this specification and valuable feedback
and implementation experience was provided by Jun-Ichiro Hagino and
Tatuya Jinmei. Other useful comments were received from Robert Elz,
Keith Moore, Elwyn Davies, Pekka Savola, and Dave Thaler. Bob Hinden
and Brian Haberman have acted as document editors during the IETF
advancement process.
This document is not the first proposal of a direct query mechanism
for address-to-name translation. The idea had been discussed briefly
in the IPng working group and RFC 1788 [19] describes such a
mechanism for IPv4.
10. References10.1. Normative References
[1] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[2] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[3] Hinden, R. and S. Deering, "Internet Protocol Version 6 (IPv6)
Addressing Architecture", RFC 3513, April 2003.
[4] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[5] Conta, A. and S. Deering, "Internet Control Message Protocol
(ICMPv6) for the Internet Protocol Version 6 (IPv6)
Specification", RFC 2463, December 1998.
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